1. Field of the Invention
The present invention relates to filters incorporating dielectric resonators, composite dielectric filters such as duplexers, and communication apparatus incorporating the same.
2. Description of the Related Art
Conventionally, for example, cellular base stations in mobile communication systems have used composite dielectric filters formed by a plurality of dielectric resonators, such as diplexers used for transmission and duplexers used for transmission and reception.
For example, Japanese Unexamined Patent Application Publication No. 10-75104 provides a dielectric filter formed by using a plurality of TM double-mode dielectric resonators. In this dielectric filter, the opening faces of the TM double-mode dielectric resonators are aligned flush with each other. A metal panel is disposed to cover the opening faces. In the panel, coupling loops are formed for inputting/outputting signals and performing coupling between the resonators. A plurality of the dielectric filters are arranged in parallel to each other to form a composite dielectric filter.
FIG. 8 shows a structural example of the composite dielectric filter according to the conventional art. In FIG. 8, the reference numerals 9 denote coaxial connectors for inputting the signals of three channels ch1, ch2, and ch3. The reference numeral 8 denotes a coaxial connector for outputting the three synthesized inputted signals. The reference characters R1a to R3c are TM double-mode dielectric resonators. These TM double-mode dielectric resonators serve as two-stage resonators by coupling between the resonance modes. In addition, coupling loops are used for performing the coupling between predetermined resonance modes of the adjacent dielectric resonators and performing the coupling between the predetermined resonance modes and the coaxial connectors. Specifically, a coupling loop 3a couples to one of the resonance modes of each of the resonators R1a, R2a, and R3a. A coupling loop 3c couples to one of the resonance modes of each of the resonators R1c, R2c, and R3c. In addition, a coupling loop 3ab performs coupling between the predetermined resonance modes of the resonators R1a and R1b, coupling between the predetermined resonance modes of the resonators R2a and R2b, and coupling between the predetermined resonance modes of the resonators R3a and R3b. Similarly, a coupling loop 3bc performs coupling between the predetermined resonance modes of the resonators R1b and R1c, coupling between the predetermined resonance modes of the resonators R2b and R2c, and coupling between the predetermined resonance modes of the resonators R3b and R3c. The above arrangement permits three dielectric filters F1, F2, and F3 to be constituted.
To adjust the characteristics of the dielectric filter, a cutting jig is inserted through adjusting holes disposed in the metal panel, and a predetermined part of a dielectric core is cut off.
However, in the composite dielectric filter according to the conventional, art as shown in FIG. 8, when the plurality of dielectric filters are arranged close to each other, the electric-fields of the coupling loops leaking from the adjusting holes are likely to easily couple to each other, whereby isolation between the adjacent filters is reduced, with the result that attenuation characteristics are deteriorated.
Accordingly, the present invention provides a dielectric filter, a composite dielectric filter, a dielectric duplexer, and a dielectric diplexer, in which isolation between adjacent filters can be obtained, and deterioration of filter characteristics can thereby be prevented. It is another object of the present invention to provide a communication apparatus incorporating one of the dielectric filter, the composite dielectric filter, the dielectric duplexer, and the dielectric diplexer.
According to a first aspect of the present invention, there is provided a composite dielectric filter including a plurality of dielectric filters, each of the dielectric filters including a dielectric resonator formed by disposing a dielectric core in a cavity, and a coupling loop for coupling to a predetermined resonance mode of the dielectric resonator. In the above composite dielectric filter, the respective dielectric resonators and coupling loops of the dielectric filters are arranged in such a manner that the directions of coupling portions of the adjacent coupling loops between the dielectric filters are substantially vertical to each other.
With this structure, even when the dielectric filters are close to each other, the adjacent coupling loops between the dielectric filters hardly couple to each other.
According to a second aspect of the present invention, there is provided a dielectric filter including a plurality of dielectric resonators formed by disposing dielectric cores in cavities, and coupling loops for coupling to predetermined resonance modes of the dielectric resonators. In this dielectric filter, the plurality of dielectric resonators are arranged in such a manner that an input signal flows in a first direction from a signal input portion, through a first series of resonators via respective coupling loops; then to a second series of resonators via a coupling loop; and then back to a signal output portion in a second direction which is opposite to the first direction, through the second series of resonators via respective coupling loops. In this arrangement of the dielectric resonators, a compact filter is obtained since the signal flows from input to output in two opposite directions, and further, the coupling loops are arranged in such a manner that the directions of coupling portions of the adjacent coupling loops are substantially vertical to each other.
With this arrangement, even in places where the dielectric resonators are adjacent to each other in the arrangement of the dielectric resonators, the coupling loops of the adjacent dielectric resonators hardly couple to each other.
According to a third aspect of the present invention, there is provided a dielectric duplexer including the composite dielectric filter or two dielectric filters that are the same as the above dielectric filter, a first-filter input port usable as a transmitted-signal input port, a second-filter output port usable as a received-signal output port, and an input/output port common to the first filter and the second filter used as an antenna port.
According to a fourth aspect of the present invention, there is provided a dielectric diplexer including the composite dielectric filter or a plurality of dielectric filters that is the same as the above dielectric filter, usable as a plurality of transmission filters for passing signals transmitted from predetermined frequency channels, and an output port common to the transmission filters usable as an antenna port.
According to a fifth aspect of the present invention, there is provided a communication apparatus including one of the composite dielectric filter, the dielectric filter, the dielectric duplexer, and the dielectric diplexer, which are described above.
Other features and advantages of the invention will be appreciated from the following detailed description of embodiments of the invention, in which like references denote like elements and parts.